'Co-axial' refers to an escapement created by Dr George Daniels, an English watchmaker. Using 4 pallet stones instead of two, it aims to reduce the amount of undesirable sliding friction in a lever escapement.
(Image credit: Wikipedia)
Widely considered to be a nice advance, the escapement is presently only used in Omega watches and I've not seen much commentary on how well its aging after a decade or so. (Introduced in 1999)